The present application is a continuation of patent application Ser. No. 10/100,012, filed Mar. 19, 2002, the entire disclosure of which is incorporated herein by reference. Priority is claimed based on Japanese patent application no. 2001-311562, filed Oct. 9, 2001.
1. Field of the Invention
The present invention relates to a water cooled inverter provided with a high heat generating power device such as an insulated gate bipolar transistor (hereinafter referred to as xe2x80x9cIGBTxe2x80x9d).
2. Description of the Prior Art
An inverter for controlling a high output motor such as a motor for a hybrid electric vehicle generally has a structure as shown in sectional schematic diagrams of FIGS. 2, 23, 25 and 26. FIG. 23 shows a conventional example of an indirect cooling structure in which a power module is fixed to a water cooled heat sink via thermal conductive grease, and FIG. 2 shows a conventional example of a direct cooling structure in which cooling water directly contacts a base plate of a power module. FIGS. 25 and 26 show improved examples of the direct cooling structure.
In the indirect cooling structure shown in FIG. 23, a metal base plate 231 of a power module 230 is fixed to an inverter case 233 integrated with a cooling fin 235 via thermal conductive grease 232, which inverter case is made of metal such as aluminum die casting.
A water channel 236 is formed by attaching a water channel cover 234 so as to cover the lower part of the inverter case 233 with. A printed circuit board (hereinafter referred to as xe2x80x9cPCBxe2x80x9d) 15 which is a control circuit board including circuit devices such as a microcontroller 16, a gate driver 17, a transformer 18 and an electrolytic capacitor 19 is placed above two power modules 230 which are placed side by side and is fixed to an inverter housing 233. A supply water channel and a drain channel to supply or drain the cooling water to/from the water channel 236 are placed at appropriate locations (not shown).
The PCB 15 is directly fixed to the inverter housing 233, but also may be attached to a support plate made of metal such as aluminum die casting and then fixed to the inverter housing 233. The upper surface of the inverter is covered with a metal cover 14.
The heat generated by a power semiconductor chip inside the power module 230 is transmitted through the base plate 231 and thermal conductive grease 232 to the fin 235, which is cooled with cooling water, and dissipated thereby. On the other hand, the heat of the circuit devices mounted on the PCB 15 is dissipated by natural convection and at the same time dissipated from through mounting section and the inverter housing 233, which inverter housing 233 is cooled with cooling water.
In the direct cooling structure shown in FIG. 2, as described in JP-A-9-207583, there are provided a water cooling opening 23 for a module in the inverter housing 21, and a metallic base 11 of a power module 10, which base is fixed to the inverter housing 21 so as to cover the opening 23.
A water channel 20 is formed by covering the bottom face of the inverter housing 21 with a water channel cover 22. In this structure, the cooling water directly contacts the metallic bases 11. By the way, the metallic base 11 is a flat plate, but may be provided with a fin. The other configurations including that of the control board are the same as those in FIG. 23, and the same reference numerals denote the same components.
The greatest advantage of the direct cooling structure over the indirect cooling structure in FIG. 23 is that it is possible to remove the grease 232 which has low thermal conductivity. This makes it possible to drastically reduce the thermal resistance from the junction of the power semiconductor chip to cooling water, namely Rth(j-w).
If thermal resistance can be reduced, it is possible to reduce a temperature amplitude xcex94T due to repetition of heating and cooling of the power semiconductor chip during operation of the inverter. This reduces distortion in the interface between the aluminum wire and power semiconductor chip electrode and distortion in the solder, and thus improves the reliability, wire life and solder life.
Furthermore, FIG. 25 and FIG. 26 show the structure of a conventional example improved in performance in comparison with the direct cooling structure in FIG. 2, by two sections orthogonal to each other. In order to improve the heat dissipation efficiency by cooling water, that is, increase thermal conductivity xe2x80x9chxe2x80x9d, it is known to increase the flow velocity of the cooling water.
However, increasing the flow velocity causes an increase in the amount of cooling water, which increases the burden on the pump circulating the cooling water. As a result, the pump capacity needs to be increased.
This leads to an increase in size of the pump, which is fatal if there are strict restrictions on the installation space and weight as in the case of an electric vehicle. Thus, it is preferable to minimize the increase in the amount of cooling water while increasing the flow velocity. This conventional example addresses this problem.
In the water channel structure 250 having an opening 252 where the power module 10 is mounted, a convex section 251 is fixed and a shallow water channel area 254 is provided in the water channel 253. Since the convex section 251 is provided only under the power module 10, a high flow velocity section only exists locally under the power module 10 and thereby can prevent an increase of pressure loss. An example similar to this conventional example is described in JP-A-4-2156, etc.
However, the conventional example shown in FIGS. 25 and 26, in which the increase of the flow velocity of cooling water is taken into account, has the following problems in the aspects of the system configuration and the cooling performance.
The depth 256 of the shallow water channel which implements high flow velocity is finally restricted by the thickness 257 of the water channel structure 250. When taking the processing accuracy of components into account, it is practically difficult to allow the convex section 251 to extend into the opening 252.
It is difficult to reduce the thickness 257 to, for example, 1 to 2 mm from the standpoint of its strength. This becomes more conspicuous in the case of an inverter having a large shape such as a high capacity inverter. Therefore, the conventional structure does not allow the flow velocity to be increased drastically while suppressing the increase of the flow rate.
Furthermore, when the height of the convex section 251 is small, the flow velocity in the area on the power module base plate 11 side in the shallow water channel area 254 is lower than that in the area on the water channel structure 250 side, and therefore the cooling water becomes easily stagnant to prevent efficient heat dissipation and to increase the temperature of the cooling water.
This adversely affects the effect of providing the convex section 251. Moreover, when the water channel structure 250 has a one-body structure as shown in FIGS. 25 and 26, the shape of the convex section 251 shown in FIG. 26 can hardly be realized in a practical sense.
When consideration is given to inserting the convex section 251 from the opening 252 and fixing there, the convex section 251 must be smaller than the opening 252. Therefore, it is impossible to significantly increase the flow velocity in the shallow water channel area 254.
Furthermore, in the case of the above-described conventional example, no consideration is given to mounting a plurality of power modules. In the case of a large capacity inverter, it is hardly imaginable to construct a system only with a single power module. This is because there is a limit to increasing the size of the module when inner stress and yield of the power module are taken into account.
In the above, heat dissipation of the power module 10 is considered. However, in the case of an apparatus such as an inverter in which a high heat generating power module and a control circuit exist, it is also important to reduce the temperature of the control circuit.
In the above-described conventional example, heat dissipation of the power module is considered, but heat dissipation of the control circuit is not considered. In this condition, even if high reliability is realized by providing high heat dissipation for only the power module, the reliability as the apparatus per se is impaired.
It is an object of the present invention to provide an inverter structure capable of increasing the flow velocity possibly while suppressing an increase in the amount of cooling water, suppressing an increase of pressure loss and therefore improving the reliability of the power module, and further to provide an inverter structure capable of significantly reducing the temperature of the control circuit in the inverter.
Main subjects of the present invention will be explained by using FIGS. 1, 4 and 24 below.
FIG. 1 is a schematic diagram of a sectional structure of a mounting area of power modules 10 which constitute an inverter. The inverter housing 13 houses two power modules 10 placed side by side and a control circuit board 15. The inverter housing 13 is covered with a top cover 14. The control circuit board 15 is provided with circuit devices such as a microcontroller 16, a gate driver 17, a transformer 18 and an electrolytic capacitor 19.
In the case where thermal conductivity is high as in the case of high flow velocity cooling, the heat transfer area need not be increased. For example, it is sufficient to provide an area about 10 times as large as the chip area of the power semiconductor generating the heat. More specifically, when the chip size is approximately 10 mm per side, a heat transfer area of about 33 mm per side is sufficient in a practical sense.
In this case, there is no longer necessity for providing a fin for the heat transfer section as in the case of the conventional examples in FIGS. 2, 25 and 26. The point is how easily and accurately a shallow water channel is formed to increase the flow velocity without increasing the flow rate.
In the present invention, by forming a shallow cavity in the inverter housing 13 and covering this cavity with the metallic bases 11 of the power modules 10, the shallow water channels 12 is formed. Water supply/drain channels 121 and 122 to supply/drain cooling water to/from the water channels 12 are provided at appropriate locations. The supply/drain channels 121 and 122 are schematically shown. The inverter housing 13 is manufactured using techniques such as press working on an aluminum plate or aluminum die casting, and therefore it is easy to accurately form a shallow cavity of, for example, 1 to 2 mm in depth.
On the other hand, a demerit of such shallow water channels 12 is that pressure loss increases because of the small cross sectional areas of the water channels. This problem is treated as follows.
As described above, in the case of cooling at high flow velocity, the heat transfer area need not be a large area, and therefore it is possible to locally place the shallow water channels 12 below the power module 10. Therefore, to reduce pressure loss, the cross-sectional area of the part of the water channel, which is not directly related to heat dissipation of the power module 10, is increased wherever possible.
FIG. 24 shows a schematic diagram of a section of this part. Unlike FIG. 1, a deep cavity is formed in the inverter housing 13 and deep water channels 240 are formed. There is no power module 10 above these water channels.
As described above, according to the present invention, a cooling water channel is constructed by forming cavities of different depths in the inverter housing 13 and by connecting these cavities. The cooling is performed in a shallow water channel formed using a shallow cavity, so that it is possible to cool with high efficiency without increasing the flow rate or pressure loss. Moreover, by placing a plurality of power modules above a plurality of shallow cavities, the present invention can also easily incorporate a plurality of power modules.
In the above-described explanations, the shallow cavities are provided on the inverter housing 13 side. On the other hand, it is also possible to provide shallow cavities on the metallic base 11 side to construct the cooling water channels 125 as shown by dotted line, or it is further possible to provide shallow cavities for both the inverter housing 13 and metallic bases 11.
Then, low temperature implementation of the control circuit will be explained using FIG. 4.
FIG. 4 shows a schematic diagram of a sectional structure of the mounting section of power modules 10. An inverter housing 42 houses two power modules 10 and a driver circuit board 40 and is covered with a top cover 14. Apart from the driver board 40, a microcontroller board 41 is housed in a bottom cover 43 located on the bottom face of the inverter housing 42. As in the above-described case, shallow water channels 12 are formed in shallow cavities in the inverter housing 42.
In this structure, the microcontroller board 41 on which microcontrollers 16, heat-sensitive parts, are mounted is thermally cut off from the inverter housing 42 on which the power modules 10 as high heating parts exist, and therefore the temperature of the microcontroller board never increases drastically.
Furthermore, while the power semiconductor modules 10 need to be placed close to the driver board 40, a relatively large distance between the microcontroller board 41 and driver board 40 causes no noise-related problem.
The features of the present invention are described above, however, features other than those described above will become more apparent from the following descriptions of preferred embodiments of the invention.
Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.